Organic working fluids

ABSTRACT

The present invention provides an improved, commercially available organic working fluid, which is operable under a broad range of temperatures, is thermally stable, has a high auto-ignition temperature, low freezing point and high critical temperature and is benign to the environment, and safe for human use. Such an organic working fluid is useful in organic Rankine cycle (ORC) power plants or units and other systems of the like; as an intermediate fluid for heat-recovery wherein heat from various heat sources is transferred using the intermediate fluid to a further working fluid and converted into work, and the intermediate fluid is also exploited to produce electricity. Such organic working fluids are also operable as heat transfer fluids either in ORC power plants or units or in other heat transfer systems. For this purpose the present invention presents a working fluid comprising at least one highly branched, heavy iso-paraffin hydrocarbons, or a mixture of two or more of such hydrocarbons. Preferably, at least one highly branched iso-paraffin hydrocarbon is present as the major component (i.e. at least 50% by volume) in the working fluid. A preferred sub-class of the class of the branched iso-paraffins which are suitable to be incorporated in organic working fluids of the present invention includes 8 to 20 carbon atom-containing hydrocarbons having at least one methyl radical (CH 3 ) arranged to achieve a highly stable compound.

FIELD OF THE INVENTION

The present invention relates to organic fluids, and more particularlyto organic fluids for use as the working fluid in high-temperatureOrganic Rankine cycle (ORC) applications and as the heat transfer fluidin heat transfer cycles for a range of low and high temperatures.

BACKGROUND

High-temperature organic working fluids have been introduced as theworking fluids in power plants and as working and heat transferintermediates in order to overcome the shortcomings of the use of thewater steam medium used for heat transfer or for waste heat recovery andpower generation. Heat-energy converters, based on the thermodynamicOrganic Rankine Circle, or similar heat-energy transfer systems, areuseful in heat recovery and power generation in particular in remotelocations, where the heat is derived from various sources, such as gasturbine exhaust gases, combustion of conventional fuels, combustion ofbiomass fuels,geothermal sources, solar heat collectors and waste heatin power plants and other industrial processes, for the purpose ofproducing electrical power in the range of from a hundred or more Watts(W) and up to a few of tens Megawatts (MW). Organic fluids sustainableat temperatures as high as about 350° C. are advantageous overwater-steam, and can be successfully utilized in power generation cycleseven at low condensing temperatures and high turbine expansion ratioswhere the use of steam may be limited due to formation of liquiddroplets at the turbine outlet due to the expansion of the steam whichmay cause erosion to the turbine blades. Because of the nature of theorganic fluids they become superheated (or dry) in the expansion processa characteristic which prevents the formation of liquid droplets as isthe case with steam. Organic fluids and their derivatives operable undera range of relatively low temperatures normally up to about 200° C. areCFCs, Freon, butane including n-butane and iso-butane, and pentane, alsoincluding the n-pentane and iso-pentane isomers. For applications wherehigher operating temperatures are required a transition was required toaromatic hydrocarbons, alkylated aromatic hydrocarbons, fluorinatedhydrocarbons such as F75 and F43 and silicone based oils. Examples arealkylated aromatic hydrocarbons are commercial Dowtherm J, which is amixture of isomers of alkylated aromatic hydrocarbon manufactured by theflow Chemical Company and Therminol LT, an alkyl substituted aromatichydrocarbon, manufactured by the Solutia Inc.

The use of the above-mentioned working fluids does have, however,several drawbacks. First, fluids such as F75 or F43 are expensive.Second, such working fluids require periodic treatment and recycling.Third, they limit operating temperatures resulting in lower efficiency.

There is, therefore, a need for a stable, commercially available organiccompound, which can be operated in its liquid and vapor states in a widerange of temperatures, thus successfully exhibiting improved performanceas a working fluid or thermal fluid for either power or electricitygenerating cycles, or heat transfer cycle.

It is therefore an object of the present invention to provide a highlythermally stable fluid useful as a working fluid for power orelectricity generating cycles or as a heat transfer fluid or heattransfer cycles, or both.

It is another object of the present invention to provide a working fluidthat has a high critical temperature and relatively low pressures atelevated temperatures.

It is another object of the present invention to provide a working fluidthat has a high auto-ignition temperature.

It is another object of the present invention to provide a working fluidthat has a low freezing or solidification temperature.

It is still another object of the present invention to provide a workingfluid that is benign to humans and to the environment.

It is still another object of the present invention to provide a workingfluid that can be easily obtainable by those in the art.

It is still another object of the present invention to provide a workingfluid that is operable in a wide range of temperatures.

It is still another object of the present invention to provide a workingfluid for use in an organic Rankine cycle for electricity or powerproduction in heat recovery applications or other heat-energy conversioncycles, and/or as a heat transfer fluid in heat transfer cycles.

It is still another object of the present invention to provide a use ofsuch a working fluid for heat and waste heat recovery from various heatsources for electricity or power generation and/or others usage of theheat.

These and other objects of the present invention will become clear asthe description proceeds.

SUMMARY OF THE INVENTION

The present invention provides an improved, commercially availableorganic working fluid, which is operable under a broad range oftemperatures, is thermally stable, has a high auto-ignition temperature,low freezing point and high critical temperature. Such an organicworking fluid is useful in organic Rankine cycle (ORC) power plants orunits and other systems of the like; as an intermediate fluid firheat-recovery wherein heat from various heat sources is transferredusing the intermediate fluid to a further working fluid and convertedinto work, and the intermediate fluid is also exploited to produceelectricity. Such organic working fluids are also operable as heattransfer fluids either in ORC power plants or units or in other heattransfer systems.

For this purpose the present invention presents a working fluidcomprising at least one highly branched, heavy iso-paraffin hydrocarbon,or a mixture of two or more of such hydrocarbons. Preferably at leastone highly branched iso-paraffin hydrocarbon is present as the majorcomponent (i.e. at least 50% by volume) in the working fluid. The highthermal stability of such hydrocarbons is provided due to the locationof the methyl radical (CH₃) arranged to achieve highly stable compounds.Such highly branched heavy iso-paraffin hydrocarbons or organic fluidshave high boiling point temperatures as well as high auto-ignitiontemperatures, and low freezing point temperatures. They exhibit highthermal stability, and in addition are benign to the environment, andsafe for human use. Their high critical temperatures enables operationat high temperatures yet below the critical temperature, by doing soachieving high cycle efficiency without the complexity associated withoperation above the critical point and at high pressure. Anotheradvantage is their commercial availability, enabling, through their use,cost effective electricity or power production from various heatsources, or heat transfer in power plants or in other uses.

A preferred sub-class of the class of the branched iso-paraffins whichare suitable to be incorporated in organic working fluids of the presentinvention includes 8 to 20 carbon atom-containing hydrocarbons having atleast one methyl radical (CH₃) arranged to achieve a highly stablecompound. Preferably, the branched iso-paraffins are highly branched;meaning that they have 3-20 methyl groups attached to tertiary orquaternary carbon atoms. As used herein, “substantially branched” meansat least 3 branched (i.e. non-end groups) methyl groups. Suchiso-paraffins, or a mixture of two or more of them, are used accordingto the present invention as the major component in working fluids inpower plants operating according to an Organic Rankine Cycle (ORC), orin any other high temperature heat recovery system, or as thermal fluidsin heat transfer cycles.

Thus, an example of the use of the working fluids of the presentinvention can be their use, according to the present invention, in aheat recovery system including a highly thermally stable working fluid,wherein the improvement comprises a highly thermally stable workingfluid suitable for operating in the range of about −50° C. up to 350°C., comprising as the major component at least one compound of formula(I):C_(n)H_(2n+2)   (I)

wherein n is between 8 and 20, and wherein the compounds of formula (I)are substantially branched.

Preferably, the above-mentioned working fluid comprises at least onecompound in which part or all the methyl groups present in said compoundare substituted with one or more halogens or halogen containingsubstituents, wherein the halogens are selected from the groupconsisting fluorine, chlorine, or bromine.

Also preferably the working fluid mentioned above further comprises anadditive selected from the group consisting of fire-retardant agents,flow aids, corrosion inhibitors, lubricants, anti-freezing agents,anti-oxidants, and process oils and mixtures thereof.

In addition, preferably, the working fluid mentioned above comprises aniso-paraffin selected from the group consisting of iso-dodecane or2,2,4,6,6-pentamethylheptane, iso-eicosane or2,2,4,4,6,6,8,10,10nonamethylundecane, iso-hexadecane or2,2,4,4,6,8,8-heptamethylnonane, iso-octane or 2,2,4 trimethylpentane,iso-nonane or 2,2,4,4 tetramethylpentane and a mixture of two or more ofthese compounds.

Another example of the use of the working fluids of the presentinvention can be their use, according to the present invention, in aheat transfer cycle including a highly thermally stable working fluid,wherein the improvement comprises a highly thermally stable workingfluid suitable for operating in the range of about −50° C. up to 350°C., comprising as the major component at least one compound of formula(I):C_(n)H_(2n+2)   (I)

wherein n is between 8 and 20, and wherein the compounds of formula (I)are substantially branched.

Preferably, the working fluid mentioned above comprises at least onecompound in which part or all the methyl groups present in said compoundare substituted with one or more halogens or halogen containingsubstituents, wherein said halogens are selected from the groupconsisting fluorine, chlorine, or bromine.

Also preferably, the work fluid mentioned above further comprises anadditive selected from the group consisting of fire-retardant agents,flow aids, corrosion inhibitors, lubricants, anti-freezing agents,anti-oxidants, and process oils and mixtures thereof.

In addition, preferably, the working fluid mentioned above comprises aniso-paraffin selected from the group consisting of iso-dodecane or2,2,4,6,6-pentamethylheptane, iso-eicosane or2,2,4,4,6,6,8,10,10-nonamethylundecane, iso-hexadecane or2,2,4,4,6,8,8-heptamethylnonane, iso-octane or 2,2,4 trimethylpentane,iso-nonane or 2,2,4,4 tetramethylpentane and a mixture of two or more ofsaid compounds.

BRIEF DESCRIPTION OF THE DRAWINGS

A description of the present inventive subject matter includingembodiments thereof is presented and with reference to the accompanyingdrawings, the description not meaning to be considered limiting in anymanner, wherein:

FIG. 1 shows an embodiment of a power plant in which the working fluidsof the present invention can be used;

FIG. 2 shows a further embodiment of a power plant in which the workingfluids of the present invention can also be used; and

FIG. 8 shows an embodiment of a portion of a power plant in which theworking fluids of the present invention can be used.

DETAILED DESCRIPTION

According to the present invention, an improved, commercially availableorganic working fluid is provided, which is operable under a broad rangeof temperatures, is thermally stable, has high critical temperature, lowfreezing or solidification temperature and has a high auto-ignitiontemperature. Such an organic working fluid is useful in Organic RankineCycle (ORC) power plants or units and other systems of the like; as anintermediate fluid for heat-recovery wherein heat from various heatsources is transferred using the intermediate fluid to a further workingfluid and converted into work, and the intermediate fluid is alsoexploited to produce electricity. Such working fluids are also operableas heat transfer fluids either in ORC power plants or units or in otherheat transfer systems.

For this purpose the present invention presents a working fluidcomprising at least one highly branched, heavy iso-parafinn hydrocarbon,or a mixture of two or more of such hydrocarbons. Preferably at leastone highly branched iso-parafin hydrocarbon is present as the majorcomponent (i.e. at least 50% by volume) in the working fluid. The highthermal stability of such hydrocarbons is provided due to the locationof the methyl radical (CH₃) arranged to achieve highly stable compounds.

Such highly branched heavy iso-paraffin hydrocarbons or organic fluidshave high boiling point temperatures as well as high auto-ignitiontemperatures, and low freezing point temperatures. They exhibit highthermal stability, and in addition are benign to the environment, andsafe for human use. Another advantage is their commercial availability,enabling, through their use, cost effective electricity or powerproduction from various heat sources, or heat transfer in power plantsor in other uses.

U.S. Pat. No. 5,612,888 discloses, inter alia, the use of iso-parafinnsas non-Newtonian liquid bearing materials as support for head componentsof a head-disk assembly over rigid disks. Such application of liquidiso-paraffins is confined to a narrow temperature range set by thetemperature operation limits of the disk driven, which may be forexample between 5° C. and 55° C.

A preferred subclass of the class of the branched iso-paraffins whichare suitable to be incorporated in organic working fluids of the presentinvention includes 8 to 20 carbon atom-containing hydrocarbons having atleast one methyl radical (CH₃) arranged to achieve a highly stablecompound. Preferably, the branched iso-paraffins are highly branched,meaning that they have 8-20 methyl groups attached to tertiary orquaternary carbon atoms. As used herein, “substantially branched” meansat least 8 branched (i.e. non-end groups) methyl groups. Suchiso-paraffins, or a mixture of two or more of them, are used accordingto the present invention as the major component in working fluids inpower plants operating according to an Organic Rankine Cycle (ORC) or inany other high temperature heat recovery system, or as thermal fluids inheat transfer cycles.

Preferred operating temperatures of the working fluids in the powerplant or heat transfer cycle are in the range of about −50° C. up toabout 350° C. Besides exhibiting thermal stability in this temperaturerange, such a wide range of operating temperatures results in improvedefficiency for the heat recovery in power plants or of heat transfer inheat transfer systems.

The branched iso-paraffins disclosed in the present invention areoptionally modified to acquire fire-retarding characteristics bysubstituting all or some of the methyl groups with one or moresubstitutents, including for example substituents such as halogens,including fluorine, chlorine, and bromine, or halogen containingsubstituents.

Preferred iso-paraffin hydrocarbons of the present invention are thecompounds according to formula (I):C_(n)H_(2n+2)   (I)where n is between 8 and 20.

The working fluids of the present invention may comprise in additionconventional additives, where such additives may be selected fromfire-retardant agents, flow aids, corrosion inhibitors, lubricants,anti-freezing agents, anti-oxidants, and process oils and mixturesthereof.

In one preferred embodiment of the present invention the branchediso-paraffin organic working fluid is, or comprises, iso-dodecane or2,2,4,6,6-pentamethylheptane.

In a second preferred embodiment of the present invention the branchediso-paraffin organic working fluid is, or comprises, iso-eicosane or2,2,4,4,6,6,8,10,10-nonamethylundecane.

In a third preferred embodiment of the present invention the branchediso-paraffin organic working fluid is iso-hexadecane or2,2,4,4,6,8,8-heptamethylnonane.

In a fourth preferred embodiment of the present invention the branchediso-paraffin organic working fluid is iso-octane or 2,2,4trimethylpentane.

In a fifth preferred embodiment of the present invention the branchediso-paraffin organic working fluid is iso-nonane or 2,2,4,4tetramethylpentane.

All of the compounds disclosed herein above are useful as majorcomponents in organic working fluids in power plants employing theRankine cycle or similar systems for heat or waste heat recovery, or inheat transfer cycles, and are thermally stable in a wide temperaturerange of about −50° C. up to about 350° C.

Non-limitative examples of energy recovering or heat transfer systemsand methods of producing power therefrom, that may employ the organiciso-paraffin fluids of the present invention, are referred to below:

As an example of an embodiment of a system in which the presentinvention can be used reference is now made to FIG. 1, and referencenumeral 10 designates an embodiment of apparatus for producing power inaccordance with the present invention. As can be seen from the drawing,the apparatus comprises intermediate fluid heater/vaporizer 12 by whichvaporized intermediate fluid is produced using heat from heat source 18e.g. using heat contained in hot gases, etc. The vaporized intermediatefluid is supplied to organic working fluid vaporizer 22 where it iscondensed by transferring heat to organic fluid present in the vaporizerso that vaporized organic fluid is produced. Intermediate fluidcondensate produced is returned to intermediate fluid heater-vaporizer12 using pump 19. The vaporized organic fluid is supplied to organicvapor turbine 24 wherein it expands and produces power. Preferably,generator 26 is driven by organic vapor turbine 24 and produceselectricity. Expanded vaporized organic fluid exiting organic vaporturbine 24 is supplied to organic fluid condenser 28 and organic fluidcondensate is produced. Pump 30 supplies organic fluid condensateexiting organic fluid condenser 28 to organic working fluid vaporizer22. In accordance with the present invention, prior to supplyingvaporized intermediate fluid exiting intermediate fluid vaporizer 12 toorganic working fluid vaporizer 22, the vaporized intermediate fluid issupplied to intermediate fluid turbine 16 wherein the vaporizedintermediate fluid expands and produces power. Also here, preferably,intermediate fluid turbine 16 drives generator 18 that produceselectricity.

In operation, intermediate fluid present in intermediate fluid vaporizer12 extracts heat from heat source 13 e.g. hot gases and, intermediatefluid vapor is produced. The intermediate fluid vapor is suppliedpreferably to intermediate fluid turbine 16 and expands thereinproducing power and expanded intermediate fluid vapor exits intermediatefluid turbine 16. Since preferably, generator 18 is coupled tointermediate fluid turbine 16 electricity is produced. Expandedintermediate fluid vapor exiting intermediate fluid turbine 16 issupplied via line or conduit 20 to organic working fluid vaporizer 22.Organic working fluid present in organic working fluid vaporizer 22extracts heat from the expanded intermediate fluid vapor andintermediate fluid condensate as well as vaporized organic working fluidis produced. Intermediate fluid condensate is supplied using pump 19 tointermediate fluid vaporizer 12. Vaporized organic working fluid issupplied to organic working fluid turbine 24 wherein it expands andpower is produced. Expanded organic working fluid vapor exits organicworking fluid turbine 24. Preferably, organic working fluid turbine 24is coupled to generator 26 and electricity is produced. The expandedorganic working fluid vapor is supplied to organic working fluidcondenser 28 that is preferably air-cooled and organic working fluidcondensate is produced. Pump 30 supplies organic working fluidcondensate to organic working fluid vaporizer 22.

The intermediate fluid mentioned in the embodiment described above canbe the organic working fluids of the present invention disclosed herein.The preferred intermediate fluid is advantageous since their use avoidsproblems of freezing, operates without being at vacuum conditions andthere is no need for chemical treatment and blow down as is usually thecase with water when used as an intermediate fluid. Preferably, theintermediate fluid is useful in a relative high temperature range:vaporizing temperature between about 250° C. and about 315° C. At thesetemperatures, the pressure of the intermediate fluid is between about 9kPa and 2600 kPa. The relatively low pressures mentioned above make thistype of fluid particularly suitable for use in the present invention.Often, the condensing temperature of the intermediate fluid on theintermediate fluid side of organic working fluid vaporizer 22 willpreferably be in the range of about 200° C. to about 120° C. but can bemuch lower if need be. Furthermore, the use of this type of intermediatefluid as a heat transfer medium for transferring heat from the heatsource to the organic working fluid and as well as producing power fromthe intermediate fluid increases the efficiency of the power producingsystem on a whole. Preferably, the organic working fluid comprisespentane, either n-pentane or iso-pentane, n-butane, iso-butane as wellas additional fluids such as hydrocarbons, for example aliphaticparaffins in their normal and isomeric form.

Furthermore, if preferred organic fluid power cycle I can include apre-heater, superheater and recuperator. In addition, if preferred,generators 18 and 26 can be replaced by a single common generator drivenby turbines 16 and 24 either using dual shaft ends in the single commongenerator or through a gear drive. Most preferred, the common generatoris interposed between turbines 16 and 24.

Referring now to FIG. 2, numeral 10A refers to a further embodiment ofan example of a system or cycle in which the organic working fluid ofthe present invention is used and which includes, as shown, arecuperator in the intermediate fluid. As can be seen from the figure,intermediate fluid vapor produced by intermediate vaporizer present inheat recovery vapor generator 40A is supplied to vapor turbine 16A forproducing power or electricity using generator 18A. Numeral 21Adesignates an intermediate fluid recuperator in which heat istransferred from expanded intermediate fluid vapor exiting intermediatefluid turbine 16A to intermediate fluid condensate supplied by pump 19Afrom the intermediate fluid side of organic working fluid vaporizer 22A.In this embodiment, portion of the intermediate fluid condensate exitingthe intermediate fluid side of organic working fluid vaporizer 22A issupplied to organic fluid pre-heater 23A for pre-heating the organicworking fluid prior to supplying it to organic working fluid vaporizer22A. A further portion of the intermediate fluid condensate exiting theintermediate fluid side of organic working fluid vaporizer 22A issupplied to intermediate fluid recuperator 21A, In the presentembodiment, heat from heat source 13A is added to the intermediate fluidcondensate exiting organic pre-heater 23A. In addition, in thisembodiment organic working fluid recuperator 27A is included and is usedfor transferring heat from expanded organic working fluid vapor exitingorganic working fluid turbine 24A to organic working fluid condensatesupplied by pump 30A from organic working fluid condenser 28A. Heatedorganic working fluid condensate exiting organic working fluidrecuperator 27A is supplied to organic working fluid pre-heater 23A.Apart from these items previously mentioned with reference to thepresent embodiment described with relation to FIG. 2, this embodiment issimilar to the embodiment described with relation to FIG. 1 and alsooperates in a similar manner.

In certain circumstances, all of the intermediate fluid exiting theintermediate fluid side of the organic working fluid vaporizer 22A canbe supplied to organic working fluid pre-heater 23A. Thereafter, thecooled intermediate fluid exiting to organic working fluid pre-heater23A can be supplied to heat source 13A, the heated intermediate fluidexiting heat source 13A being supplied to intermediate fluid recuperator21A.

In FIG. 2, generator 18A is preferably shared by the output ofintermediate turbine 16A and organic working fluid turbine 24A. This isbecause intermediate turbine 16A can operate efficiently at relativelylow rotational speeds (1500-1800 RPM), permitting it to be directlycoupled to generator 18A whose rotational speed also is relatively low(1500-1800 RPM). Similarly, the rotational speed of organic workingfluid turbine 24A can also be relatively low (1600-1800 RPM), permittingit also to be directly coupled to generator 18E. Thus generator 18A isinterposed between intermediate turbine 16A and organic working fluidturbine 24A. However, if preferred, separate generators can be provided.

Furthermore, preferably, the embodiment described with reference to FIG.2 comprises two separate entities, heat source unit or heat recoveryvapor generator 40A and power cycle unit 50A.

As mentioned above, the intermediate fluid of the embodiment shown inFIG. 2 can be the organic working of the present invention.

It is to be pointed out that the intermediate fluid specified above canbe used for all the embodiments mentioned herein.

Examples of heat sources from which the present invention can extractheat from are waste heat from gas turbines, waste heat from otherindustrial processes, waste heat produced in cement manufacture and inthe cement manufacturing industry, heat produced by the combustion ofconventional fuels, heat produced by the combustion of biomass fuel,geothermal resources including geothermal steam and geothermal liquid,solar energy, etc. In addition, the present invention can be used e.g.for producing electrical power in the range of from about a hundred ormore Watts (W) up to a few tens of Megawatts (MW).

Furthermore, while this specification refers to the heat transfer cycleas using an intermediate fluid, it is possible to consider, inaccordance with the present invention, the cycle using the intermediatefluid, when referring to power production, as a topping cycle with theorganic working fluid cycle as a bottoming cycle.

Moreover, while the embodiments of the present invention describe theuse of generators 18 and 26 or the use of a common generator forproducing electricity, in accordance with the present invention, thepower produced by turbines 16 and 24 or either of them can be used asmechanical power. Thus, for example, they can run a compressor, otherloads, etc.

Also in this embodiment, the intermediate fluid can be the organicworking fluids of the present invention disclosed herein.

Furthermore, it is to be pointed out that while the intermediate fluidspecified above is described as operating in a cycle wherein theintermediate fluid transfers heat from the heat source to a furtherorganic working fluid, the organic working fluid of the presentinvention can be used in accordance with the present invention in such apower cycle wherein the intermediate fluid is used in a power cyclewithout transferring heat to a farther organic working fluid.

In a further preferred embodiment of the present invention, the organicworking fluids of the present invention may be used for producing poweror electricity from a heat source such as solar energy wherein theorganic fluids disclosed in the present invention may be used in a powerplant operating according to the organic Rankine cycle (see FIG. 3). Insuch a case, these organic working fluids are heated preferably in solarcollector 40B such as a solar trough collector 42B and then supplied toa flash chamber, tank or vaporizer 44B for producing organic vapor whichis supplied to a vapor turbine of an organic Rankine cycle (ORC) powerplant for producing power or electricity. Liquid working fluid from theflash tank is not flashed is recycled to solar collector 40B either tothe inlet of a single solar collector (not shown) or to the inlet of thesecond solar collector of a pair of serially connected solar collectors.Thereafter, the expanded organic working fluid is condensed in acondenser and the organic working fluid condensate is returned from theorganic Rankine cycle (ORC) power plant to the solar collector.

Further non-limitative examples of energy or heat recovering or heattransfer systems and methods of producing power therefrom, that mayemploy the organic iso-paraffin fluids of the present invention,disclosed in several former publications, are all incorporated herein byreference:

In one preferred embodiment of the present invention the organiciso-paraffin fluids may be employed in vapor turbines and in a methodfor the operation of vapor turbines thereof applying a heat recuperatorin ORC power plants or units, as disclosed in U.S. Pat. No. 3,040,528.

In a second preferred embodiment of the present invention the sameorganic fluids may be employed in power plants applying cascaded vaporturbines and in a method thereof as disclosed in EP 1 174 590 preferablyusing the same organic fluid as the intermediate fluid. In such systemsand methods thereof a vaporized intermediate, as for example an organic,alkylated heat transfer fluid, preferably a synthetic alkylated aromaticheat transfer fluid, is used as the primary recipient of heat from theheat source, transferring it afterwards to the organic fluid.

In a third preferred embodiment of the present invention, as disclosedin U.S. Pat. No. 4,760,705, the organic fluids of the present inventionmay be employed as the working fluid or intermediate working fluid inRankine cycle power plant disclosed therein wherein in this patent animproved working fluid useful in power plants selected from the groupconsisting bicyclic aromatic hydrocarbons, substituted bicyclic aromatichydrocarbons, heterocyclic bicyclic aromatic hydrocarbons, substitutedheterocyclic bicyclic aromatic hydrocarbons, bicyclic or heterocycliccompounds where one ring is aromatic and the other condensed ring isnon-aromatic, and their mixtures are disclosed. In a further aspect ofthis U.S. patent a binary Rankine cycle power plant is provided in whichthe condenser of the high temperature and pressure turbine is cooled bya different working fluid which is vaporized thereby and supplied to alow temperature and turbine.

In a fourth preferred embodiment of the present invention, as disclosedin U.S. Pat. No. 6,701,712, the organic fluids of the present inventionmay be employed in a method and apparatus of producing power whereinheat received from a hot-air clinker process in cement factories istransferred to a heat transfer fluid, e.g. thermal oil in an air-heattransfer fluid heat-exchanger and the heat is used to vaporize organicfluid in a vaporizer for power production using the vaporized workingfluid in a turbine,

In a fifth preferred embodiment of the present invention, the organicfluids of the present invention may be employed in a heat recoverymethod and system thereof according to U.S. Pat. No. 6,571,548, whereinheat emitted from a heat source, such as a gas turbine is transferred toan intermediate fluid, that can be pressurized water, which transfersthe heat to an organic working fluid. Vaporized organic fluid producedthereby is then used to drive an organic fluid turbine for producingpower by using at electric generator connected to the organic fluidturbine.

In a sixth preferred embodiment of the present invention, the organicfluids of the present invention may be employed in a power plantoperating according to gas turbine system disclosed in U.S. Pat. No.5,687,570. According to this system a water-based, closed loop Rankinecycle power plant is included. Also, according to this system, the steamcondenser of the water-based, closed loop Rankine cycle power plant iscooled by organic fluid condensate which is thus pro-heated and thensupplied to the organic fluid vaporizer, the organic fluid vaporproduced thereby operating an organic vapor turbine. In severalembodiments included in this patent, the steam condenser operates as anorganic fluid vaporizer.

In a seventh preferred embodiment of the present invention, the organicfluids of the present invention may be employed in a power plantoperating on steam according to methods of operation and powerproduction thereof disclosed in U.S. Pat. No. 5,497,624. This system andmethod includes apparatus for producing power using geothermal fluidsuch that geothermal steam produces power in a steam turbine, andexpanded geothermal steam vaporizes organic fluid for producingadditional power in a closed organic Rankine cycle turbine bothcontained in each of a plurality of integrated power plant unit modules.Furthermore, means for compressing non-condensable gases present in thesteam condensers contained in each power plant module can be providedsuch that the compressed non-condensable gases can be vented into are-injection well together with pressurized steam condensate produced inthe steam condensers. Moreover, geothermal liquid contained in thegeothermal fluid can be re-injected into the re-injection well.

In an eigth preferred embodiment of the present invention disclosed inU.S. Pat. No. 4,642,625, the organic fluids of the present invention maybe employed in a closed Rankine cycle power plant or unit operatingtogether with a geothermal steam turbine for producing power.

In a ninth preferred embodiment of the present invention, disclosed inU.S. Pat. No. 4,700,548, the organic fluids of the present invention maybe employed in a heat recovery cascaded power plant and a method forproducing power. The power plant integrates a plurality of independentclosed Rankine cycle units operating serially, wherein a low to mediumtemperature source fluid, such as for example an industrial fluid orgeothermal fluid is applied serially to the vaporizer of closed Rankinecycle units producing heat depleted source fluid and the heat depletedsource fluid is applied to all of the pre-heaters in parallel wherein apre-heater is provided for each vaporizer.

In a tenth preferred embodiment of the present invention, disclosed inU.S. Pat. No. 4,578,958, the organic fluids of the present invention maybe employed in serially operating integrated closed Rankine cycle powerplants, having advantageously a better efficiency in heat recovery andpower production. In the serially operating integrated closed Rankinecycle power plants, a low to medium temperature source fluid, such asfor example an industrial fluid or geothermal fluid is applied seriallyto the vaporizer of closed Rankine cycle units producing heat depletedsource fluid and the heat depleted source fluid is applied to all of thepre-heaters in parallel wherein a pre-heater is provided for eachvaporizer.

In an eleventh preferred embodiment of the present invention, disclosedin U.S. Pat. No. 4,551,980, the organic fluids of the present inventionmay be employed in the hybrid power plant disclosed therein. Such ahybrid system is disclosed in Closed Cycle Vapor Turbogenerator—AReliable Remote Prime Power Source” by N. S. Christopher and J. Gropper,presented at the International Telecommunications Energy Conference inWash., D.C. October 1982, pages 443-449. The hybrid power plantdisclosed in U.S. Pat. No. 4,551,980 includes an intermittently operablenon-fuel consuming power generator, such as a photovoltaic cell array,or a wind generator, connected through a control-circuit to a batteryfor charging the same during operation of the power generator and forsupplying current to a time-wise, substantially constant, electricalload. In addition, the hybrid power plant includes an electric generatorconnected to an intermittently operable prime mover for charging thebattery and supplying power to the electrical load when the prime moveris operated. According to this patent, the prime mover can be a Rankinecycle organic fluid vapor turbogenerator or power unit or power plantemploying the Rankine cycle using the organic working fluid including avaporizer and a burner such as that described in U.S. Pat. No. 3,409,782and in “Considerations for evaluating, maintaining pipe line coatings”,Duane Tracey, PIPE LINE & GAS INDUSTRY, August 1997 and “Two Decades ofSecurity Along TranAlaska Pipeline”, Frichtl, W., Pipeline & GasJournal, July, 1997.

In a twelvth preferred embodiment of the present invention, disclosed inU.S. patent application Ser. No. 10/470,800, the organic fluids of thepresent invention may be employed in the Rankine cycle turbine includedin the uninterruptible power supply and the method for supplyinguninterruptible power to a load disclosed therein. This method forsupplying interruptible power to a load connected to a power linecomprises connecting the power line to a rotatable member comprising aRankine cycle turbine coupled to device that preferably operates as amotor when line power is applied to the device thereby rotating themember at a standby rotational speed for storing a predetermined amountof kinetic energy in the rotating member, and that operates as agenerator when line power is inoperative, the member being rotated bythe application of vaporized working fluid to the turbine. Additionally,the method includes vaporizing working fluid and maintaining the same atan operational temperature level only when the line power is inoperable.Furthermore, the method includes holding working fluid at a standbytemperature level while the power line is operative, the standbytemperature level preferably being greater than the operationaltemperature level whereby the working fluid contains a predeterminedamount of stored thermal energy while the power line is operative. Inaddition, the method includes applying the vaporized working fluid tothe turbine thereby rotating the rotatable member in response to loss ofline power whereby the turbine rotates the member at a nominal speedless than the standby rotational speed. Moreover, the method includesconnecting the device to the load whereby power is supplied to the loadwhile the power line is inoperative so that the stored the thermalenergy in the working fluid and the predetermined amount of kineticenergy are converted to power for the load upon loss of line power. TheRankine cycle turbine disclosed in this U.S. patent application isincluded in a Rankine cycle turbine system which also includes a boiler,a burner, a condenser, a working fluid supply to the bearings includinga reservoir for lubricating the bearings, and working fluid cycle pump,e.g. a pitot pump.

In addition, it should be noted that means mentioned in thisspecification refer to suitable means for carrying out the presentinvention.

Furthermore, it should be pointed out that the present inventionincludes as well the method for operating the apparatus disclosed withreference to above-described figures.

All the above description has been provided for the purpose ofillustration and is not meant to limit the invention in a way. As willbe apparent to a skilled person, the invention can be carried out byusing different compounds, all without exceeding the scope of theinvention.

All references, patents, applications, tests, standards, documents,publications, brochures, texts, articles, etc. mentioned herein areincorporated by reference. Where a numerical limit or range is stated,the endpoints are included. Also, all values and subranges within anumerical limit or range are specifically included as if explicitlywritten out.

All the above description and examples have been provided for thepurpose of illustration and are not meant to limit the invention in anyway. As will be apparent to a skilled person, the invention can becarried out in using different compounds, all without exceeding thescope of the invention.

1. In a heat recovery system including a highly thermally stable workingfluid, wherein the improvement comprises a highly thermally stableworking fluid suitable for operating in the range of about −50° C. up to350° C., comprising as the major component at least one compound offormula (I):C_(n)H_(2n+2)   (I) wherein n is between 8 and 20, and wherein thecompounds of formula (I) are substantially branched.
 2. A fluidaccording to claim 1, comprising at least one compound in which part orall the methyl groups present in said compound are substituted with oneor more halogens or halogen containing substituents, wherein saidhalogens are selected from the group consisting fluorine, chlorine, orbromine.
 3. A fluid according to claim 1, further comprising an additiveselected from the group consisting of fire-retardant agents, flow aids,corrosion inhibitors, lubricants, anti-freezing agents, anti-oxidants,and process oils and mixtures thereof.
 4. A fluid according to claim 1,wherein said fluid comprises an iso-parafinn selected from the groupconsisting of iso-dodecane or 2,2,4,6,6-pentamethylheptane, iso-eicosaneor 2,2,4,4,6,6,8,10,10-nonamethylundecane, iso-hexadecane or2,2,4,4,6,8,8-heptamethylnonane, iso-octane or 2,2,4 trimethylpentane,iso-nonane or 2,2,4,4 tetramethylpentane and a mixture of two or more ofsaid compounds.
 5. The heat recovery system of claim 1, wherein saidheat recovery system is a heat recovery organic Rankine cycle (ORC)power plant.
 6. The heat recovery system of claim 5, wherein said heatrecovery system comprises an intermediate fluid, which is said highlythermally stable working fluid and wherein said intermediate fluidtransfers heat from a heat source to a further organic working fluid forproducing power, and said intermediate fluid is also used for producingpower.
 7. The heat recovery system of claim 6 wherein both theintermediate fluid and further organic working fluid operate power cycleoperating according to the Rankine cycle.
 8. A method for waste heatrecovery from a power plant, comprising extracting heat from the wasteheat source using a power plant operated by the highly thermally stableworking fluid of claim
 1. 9. A method for waste heat recovery from wasteheat from industrial processes, comprising extracting heat from thewaste heat source using a power plant operated by the highly thermallystable working fluid of claim
 1. 10. A method for heat recovery fromheat produced by the combustion of conventional fuels, comprisingextracting heat produced by the combustion of conventional fuels using apower plant operated by the highly thermally stable working fluid ofclaim
 1. 11. A method for heat recovery from a geothermal heat source,comprising extracting heat from the geothermal heat source using a powerplant operated by the highly thermally stable working fluid of claim 1.12. A method for heat recovery from solar radiation, comprisingextracting heat from a heat source produced by solar energy using apower plant operated by the highly thermally stable working fluid ofclaim
 1. 13. The use of a working fluid of any of claims 1 to 4 in wasteheat recovery in power plants.
 14. The use of a working fluid of any oneof claims 1 to 4 in heat recovery of geothermal sources.
 15. The use ofa working fluid of any one of claims 1 to 4 in heat recovery of a heatsource produced from solar energy.
 16. The use according to claim 15 ofa working fluid in heat recovery of a heat source produced by solarenergy wherein said working fluid is heated in a solar trough collectorand supplied to a flash vaporizer for producing vapor that is suppliedto a vapor turbine.
 17. In a heat transfer cycle including a highlythermally stable working fluid, wherein the improvement comprises ahighly thermally stable working fluid suitable for operating in therange of about −50° C. up to 350° C., comprising as the major componentat least one compound of formula (I):C_(n)H_(2n+2)   (I) wherein n is between 8 and 20, and wherein thecompounds of formula (I) are substantially branched.
 18. A fluidaccording to claim 17, comprising at least one compound in which part orall the methyl groups present in said compound are substituted with oneor more halogens or halogen containing substituents, wherein saidhalogens are selected from the group consisting fluorine, chlorine, orbromine.
 19. A fluid according to claim 17, further comprising anadditive selected from the group consisting of fire-retardant agents,flow aids, corrosion inhibitors, lubricants, anti-freezing agents,anti-oxidants, and process oils and mixtures thereof.
 20. A fluidaccording to claim 17, wherein said fluid comprises an iso-paraffinselected from the group consisting of iso-dodecane or2,2,4,6,6-pentamethylheptane, iso-eicosane or2,2,4,4,6,6,8,10,10-nonamethylundecane, iso-hexadecane or2,2,4,4,6,8,8-heptamethylnonane, iso-octane or 2,2,4 trimethylpentane,iso-nonane or 2,2,4,4 tetramethylpentane and a mixture of two or more ofsaid compounds.
 21. The use of a working fluid of any of claims 17 to 20in heat transfer cycles.
 22. An organic Rankine cycle power plantcomprising a vaporizer for producing organic working fluid vapor, avapor turbine for expanding said organic working fluid vapor, anelectric generator driven by said vapor turbine for producing electricalpower, a condenser for condensing expanded organic working fluid vaporexiting said vapor turbine and a pump for supplying the organic workingfluid condensate produced by said condenser to said vaporizer, saidorganic working fluid comprising a highly thermally stable working fluidsuitable for operating in the range of about −50° C. up to 350° C.,comprising as the major component at least one compound of formula (I):C_(n)H_(2n+2)   (I) wherein n is between 8 and 20, and wherein thecompounds of formula (I) an substantially branched.
 23. The organicRankine cycle power plant according to claim 22 wherein said vaporizerreceives heat from power plant waste heat.
 24. The organic Rankine cyclepower plant according to claim 22 wherein said power plant comprises aheat recovery organic Rankine cycle (ORC) power plant for recoveringheat from power plant waste heat.
 25. The organic Rankine cycle powerplant according to claim 22 wherein said power plant comprises a heatrecovery organic Rankine cycle (ORC) power plant for recovering heatfrom geothermal sources.
 26. The organic Rankine cycle power plantaccording to claim 22 wherein said power plant comprises a heat recoveryorganic Rankine cycle (ORC) power plant for recovering heat from a heatsource produced from solar energy.
 27. The organic Rankine cycle powerplant according to claim 26 wherein said organic Rankine cycle powerplant further comprises a pre-heater for pre-heating the organic workingfluid with geothermal fluid prior to supplying it to said vaporizer. 28.Apparatus for producing power comprising a plurality of organic Rankinecycle power plants according to claim 27 each including a pre-heater andvaporizer wherein said geothermal fluid is applied in series to thevaporizers of said plurality of said organic Rankine cycle power plantsproducing heat depleted geothermal fluid and the heat depletedgeothermal fluid is applied in parallel to the pre-heaters of saidplurality of said organic Rankine cycle power plants.
 29. The organicRankine cycle power plant according to claim 25 wherein said organicRankine Canine cycle power plant operates together with a geothermalsteam turbine.
 30. The organic Rankine cycle power plant according toclaim 29 further including means for re-injecting steam condensate,non-condensable gases and geothermal liquid into a re-injection well.31. The organic Rankine cycle power plant according to claim 22 furthercomprising a burner.
 32. The organic Rankine cycle power plant accordingto claim 22 wherein said power plant comprises an intermediate fluid,which is said highly thermally stable working fluid and wherein saidintermediate fluid transfers heat from a heat source to a furtherorganic working fluid for producing power, and said intermediate fluidis also used or producing power.
 33. The organic Rankine cycle powerplant according to claim 32 further comprising a recuperator for heatingcondensate of said further organic working fluid with further organicworking fluid vapor exiting a vapor turbine operated by said furtherorganic working fluid prior to supplying said further organic workingfluid vapor exiting said vapor turbine to a further organic workingfluid condenser.
 34. The organic Rankine cycle power plant according toclaim 32 further comprising a further organic vapor turbine forexpanding further organic vapor turbine vapor produced from heattransferred from said intermediate fluid and producing power.
 35. Theorganic Rankine cycle power plant according to claim 34 furthercomprising an electric generator run by said further organic vaporturbine for producing electricity.
 36. The organic Rankine cycle powerplant according to claim 35 wherein said electric generator is run byboth said vapor turbine operated by said intermediate fluid and saidfurther organic vapor turbine.
 37. The organic Rankine cycle power plantaccording to claim 26 wherein said vaporizer is a flash vaporizersupplied with said working fluid heated in a solar trough collector forproducing vapor that is supplied to said vapor turbine.
 38. The organicRankine cycle power plant according to claim 22 further comprising arecuperator for heating condensate of said organic working fluid withorganic working fluid vapor exiting said vapor turbine prior tosupplying said organic working fluid vapor exiting said vapor turbine tosaid condenser.